BIONOMICS 207 



peculiarity of this kind is "Osmosis," the widespread but 

 ''not yet fully understood" phenomena showing a double 

 transfer of solutions of different densities when on opposite 

 sides of a permeable (especially colloidal) system. " Yery 

 many of the conspicuous changes of form undergone by 

 organic germs, are due mainly to the permeation of their 

 limiting membranes by the surrounding liquids." 



What is omitted, however, is that, as we have seen, proto- 

 plasm makes its own adaptations, its own osmotic arrange- 

 ments, and selects its own food ; on which selection indeed the 

 subsequent osmotic arrangements are largely dependent. The 

 living substance of the plant, for instance, secretes over its 

 surface a skin of cellulose, or some analogous substance, whilst, 

 broadh^ speaking, that of the animal does not, and this 

 difference, as Prof. Bretland Farmer says : " from the start 

 was fraught with consequences of the greatest importance, and 

 has profoundly affected the entire course of development in 

 the two Kingdoms respectively." 



This difference we have to regard, I believe, as an early 

 protoplasmic adaptation in accordance with bio-economic 

 requirements, i.e., with those of biological symbiosis. It was 

 in the course of symbiogenetic evolution that the plant formed 

 its important character for work which has remained for all 

 these ages the outstanding feature of plant-life. That the 

 plant at the same time remained sensitive to many mechanical 

 and quasi-mechanical forces, that it had to adapt itself to vary- 

 ing conditions of osmosis is, of course, true, but evidently all 

 mechanical adaptations are subordinate to a fundamental bio- 

 economic adaptation. 



Exceptions are supplied by cases coming under the head 

 of "extreme determination," i.e., biological abnormalities 

 due, as already explained, to a swerving from the path of 

 bio-economic usefulness. These exceptions, however, may be 

 said to confirm the rule. It is only in pathological cases that 

 an organism precisely because of loss of character becomes 

 "extremely determined" by mechanical factors. It is indeed 



